PRELIMINARY ESTIMATES OF POPULATION-SIZE AND CAPTURE RATES OF MATURE ACANTHOPAGRUS-BERDA IN THE KOSI LAKES SYSTEM, SOUTH-AFRICA, USING MARK-RECAPTURE METHODS

Population size estimates and capture rates by various fishing techniq ues of mature estuarine bream, Acanthopagrus berda, were determined in the Kosi lakes system using mark-recapture methods. The total populat ion size of mature A. berda was estimated to be 45 257 (95% confidence interval: 31 589-74 429) based on fish recaptured in fish traps and 5 6 112 (95% confidence interval: 25 505-374 080) using recaptures from recreational anglers. Fish traps were estimated to catch about 5% of t he mature population of A. berda annually, while recreational rod and line angling and traditional spearfishing accounted for about 1% and 0 .2% of the mature population respectively. Limited mark-recapture data for other species of fishes in the lakes yielded annual capture rates by fish traps ranging from 2.4% to 5.8%. These levels of fishing appe ar low enough to be sustainable, but evidence from a long-term monitor ing programme indicates an increase in overall fishing effort in the K osi lakes between 1984 and 1996 and a three-fold increase in the propo rtion of the A. berda population caught annually. However, there is no evidence from available catch per unit effort (CPUE) data that curren t levels of harvesting of A. berda are unsustainable. This needs to be confirmed through modelling of the A. berda stocks and continued moni toring of CPUE in all components of the Kosi lakes fishery. In the mea ntime, an increase in fishing effort directed at this species is not r ecommended.